In the presence of a catalytic amount of Fe(CO)5, terminal acetylenes, isocyanates and CO undergo [2 + 2 + 1] cyclization to form substituted maleimides and hydantoins; when internal alkynes are used, exclusive maleimide formation is observed. While the maleimides can be obtained as the major products, in up to 90% yield, when the reaction is carried out in CO atmosphere, in absence of CO, the hydantoins are formed in up to 87% yield. Formation of maleimides has been shown to occur via the formation of a ferrole intermediate, whereas the hydantoins are proposed to form through successive insertion of isocyanate into the iron–acetylide bond. All compounds were characterized by spectroscopic methods and molecular structures of some compounds were established by single crystal X-ray diffraction method.
在催化量的Fe(CO)5存在下,末端
炔烃、
异氰酸酯和CO发生[2 + 2 + 1]环化反应形成取代的马来
酰亚胺和
氢腺嘌呤;当使用内
烯炔时,观察到只形成马来
酰亚胺。虽然在CO气氛中进行反应时,马来
酰亚胺可以作为主要产物获得,产率高达90%,但在没有CO的情况下,
氢腺嘌呤的产率可达87%。已显示马来
酰亚胺的形成通过形成
铁酰基
中间体进行,而
氢腺嘌呤则被提议通过
异氰酸酯逐步插入到
铁-炔基键中形成。所有化合物均通过光谱方法进行表征,部分化合物的分子结构通过单晶X射线衍射方法建立。